stb_image: fix warnings

stb_image.h

@@ -1,4 +1,4 @@
-/* stb_image - v2.17b - public domain image loader - http://nothings.org/stb
+/* stb_image - v2.18 - public domain image loader - http://nothings.org/stb
                                   no warranty implied; use at your own risk
 
    Do this:
@@ -48,6 +48,7 @@ LICENSE
 
 RECENT REVISION HISTORY:
 
+      2.18  (2018-01-30) fix warnings
       2.17  (2018-01-29) bugfix, 1-bit BMP, 16-bitness query, fix warnings
       2.16  (2017-07-23) all functions have 16-bit variants; optimizations; bugfixes
       2.15  (2017-03-18) fix png-1,2,4; all Imagenet JPGs; no runtime SSE detection on GCC
@@ -1330,10 +1331,11 @@ STBIDEF int      stbi_is_hdr          (char const *filename)
    return result;
 }
 
-STBIDEF int      stbi_is_hdr_from_file(FILE *f)
+STBIDEF int stbi_is_hdr_from_file(FILE *f)
 {
    #ifndef STBI_NO_HDR
-   long pos = ftell(f), res;
+   long pos = ftell(f);
+   int res;
    stbi__context s;
    stbi__start_file(&s,f);
    res = stbi__hdr_test(&s);
@@ -2213,7 +2215,7 @@ static void stbi__idct_block(stbi_uc *out, int out_stride, short data[64])
          //    (1|2|3|4|5|6|7)==0          0     seconds
          //    all separate               -0.047 seconds
          //    1 && 2|3 && 4|5 && 6|7:    -0.047 seconds
-         int dcterm = d[0] << 2;
+         int dcterm = d[0]*4;
          v[0] = v[8] = v[16] = v[24] = v[32] = v[40] = v[48] = v[56] = dcterm;
       } else {
          STBI__IDCT_1D(d[ 0],d[ 8],d[16],d[24],d[32],d[40],d[48],d[56])