Cleanup: remove redundant NULL checks in ImFileType.is_a callback

Most of these callbacks don't do a NULL check,
so there is no need to do this for bmp/png.

Also correct radiance_hdr comments.

source/blender/imbuf/intern/bmp.c

@@ -74,31 +74,27 @@ typedef struct BMPHEADER {
 
 static int checkbmp(const uchar *mem)
 {
+  if (!CHECK_HEADER_FIELD_BMP(mem)) {
+    return 0;
+  }
 
   int ret_val = 0;
   BMPINFOHEADER bmi;
   uint u;
 
-  if (mem) {
-    if (CHECK_HEADER_FIELD_BMP(mem)) {
-      /* skip fileheader */
-      mem += BMP_FILEHEADER_SIZE;
-    }
-    else {
-      return 0;
-    }
+  /* skip fileheader */
+  mem += BMP_FILEHEADER_SIZE;
 
-    /* for systems where an int needs to be 4 bytes aligned */
-    memcpy(&bmi, mem, sizeof(bmi));
+  /* for systems where an int needs to be 4 bytes aligned */
+  memcpy(&bmi, mem, sizeof(bmi));
 
-    u = LITTLE_LONG(bmi.biSize);
-    /* we only support uncompressed images for now. */
-    if (u >= sizeof(BMPINFOHEADER)) {
-      if (bmi.biCompression == 0) {
-        u = LITTLE_SHORT(bmi.biBitCount);
-        if (u > 0 && u <= 32) {
-          ret_val = 1;
-        }
+  u = LITTLE_LONG(bmi.biSize);
+  /* we only support uncompressed images for now. */
+  if (u >= sizeof(BMPINFOHEADER)) {
+    if (bmi.biCompression == 0) {
+      u = LITTLE_SHORT(bmi.biBitCount);
+      if (u > 0 && u <= 32) {
+        ret_val = 1;
       }
     }
   }

source/blender/imbuf/intern/png.c

@@ -63,14 +63,13 @@ int imb_is_a_png(const unsigned char *mem)
 {
   int ret_val = 0;
 
-  if (mem) {
 #if (PNG_LIBPNG_VER_MAJOR == 1) && (PNG_LIBPNG_VER_MINOR == 2)
-    /* Older version of libpng doesn't use const pointer to memory. */
-    ret_val = !png_sig_cmp((png_bytep)mem, 0, 8);
+  /* Older version of libpng doesn't use const pointer to memory. */
+  ret_val = !png_sig_cmp((png_bytep)mem, 0, 8);
 #else
-    ret_val = !png_sig_cmp(mem, 0, 8);
+  ret_val = !png_sig_cmp(mem, 0, 8);
 #endif
-  }
+
   return ret_val;
 }
 

source/blender/imbuf/intern/radiance_hdr.c

@@ -199,15 +199,17 @@ static void FLOAT2RGBE(const fCOLOR fcol, RGBE rgbe)
 
 int imb_is_a_hdr(const unsigned char *buf)
 {
-  /* For recognition, Blender only loads first 32 bytes, so use #?RADIANCE id instead */
-  /* update: actually, the 'RADIANCE' part is just an optional program name,
-   * the magic word is really only the '#?' part */
-  // if (strstr((char *)buf, "#?RADIANCE")) return 1;
-  if (memcmp((char *)buf, "#?", 2) == 0) {
-    return 1;
-  }
-  // if (strstr((char *)buf, "32-bit_rle_rgbe")) return 1;
-  return 0;
+  /* NOTE: `#?RADIANCE` is used by other programs such as `ImageMagik`,
+   * Although there are some files in the wild that only use `#?` (from looking online).
+   * If this is ever a problem we could check for the longer header since this is part of the spec.
+   *
+   * We could check `32-bit_rle_rgbe` or `32-bit_rle_xyze` too since this is part of the format.
+   * Currently this isn't needed.
+   *
+   * See: http://paulbourke.net/dataformats/pic/
+   */
+  const unsigned char magic[2] = {'#', '?'};
+  return memcmp(buf, magic, sizeof(magic)) == 0;
 }
 
 struct ImBuf *imb_loadhdr(const unsigned char *mem,
@@ -224,7 +226,7 @@ struct ImBuf *imb_loadhdr(const unsigned char *mem,
   const unsigned char *ptr, *mem_eof = mem + size;
   char oriY[80], oriX[80];
 
-  if (imb_is_a_hdr((void *)mem)) {
+  if (imb_is_a_hdr(mem)) {
     colorspace_set_default_role(colorspace, IM_MAX_SPACE, COLOR_ROLE_DEFAULT_FLOAT);
 
     /* find empty line, next line is resolution info */

source/blender/imbuf/intern/targa.c

@@ -288,7 +288,7 @@ static bool dumptarga(struct ImBuf *ibuf, FILE *file)
 
 int imb_savetarga(struct ImBuf *ibuf, const char *filepath, int flags)
 {
-  char buf[20] = {0};
+  char buf[18] = {0};
   FILE *fildes;
   bool ok = false;