glTexImage2D slicing and alignment issues appearing in window

I'm working on making my own topographic map, and I have been using .hgt files from NASA.

I'm loading the files using

void MapImage::load_map_file(const char* filename) {
    std::ifstream file(filename, std::ios::in | std::ios::binary);
    if (!file) {
        std::cout << "Error opening file!" << std::endl;
    }
    std::vector<short> tempHeight(TOTAL_SIZE);
    unsigned char buffer[2];

    int x, y;
    for (int i = 0; i < TOTAL_SIZE; i++) {
        if (!file.read(reinterpret_cast<char*>(buffer), sizeof(buffer))) {
            std::cout << "Error reading file!" << std::endl;
        }
        tempHeight[i] = (buffer[0] << 8) | buffer[1];
    }

    height = tempHeight;
}

And then adding them to an inmemory bitmap using:

void MapImage::loadTextureImage() {
img_tex = 0;
glGenTextures(1, &img_tex);

int x, y, w, h;
w = h = SRTM_SIZE;
unsigned char* img;
img = (unsigned char *)malloc(3 * w * h);
memset(img, 0, sizeof(img));

int g = 0;
double height_color;

/*
for(int i = 0; i < TOTAL_SIZE; i++){
    height_color = (float)height[i] / 10.0;
    g = (height_color * 255);
    if (g>255)g = 255;

    img[i * 3 + 2] = (unsigned char)0;
    img[i * 3 + 1] = (unsigned char)g;
    img[i * 3 + 0]= (unsigned char)0;
}
*/

for (int i = 0; i < w; i++) {
    for (int j = 0; j < h; ++j) {
        x = i; 
        y = (h - 1) - j;

        height_color = (float)height[j + (i * w)] / 10.0;
        g = (height_color * 255);
        if (g>255)g = 255;

        img[(x + y*w) * 3 + 2] = (unsigned char)0;
        img[(x + y*w) * 3 + 1] = (unsigned char)g;
        img[(x + y*w) * 3]     = (unsigned char)0;
    }
}


glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, img_tex);

glTexImage2D(
    GL_TEXTURE_2D,
    0,
    GL_RGB,
    w,
    h,
    0,
    GL_RGB,
    GL_UNSIGNED_BYTE,
    img
);
}

However this results in a image with the corner sliced, like this

Using the commented version in the loadTextureImage() looks slightly different, however with the same corner sliced.

Does anyone have a hint to whats going on? I've tried using a image as a texture, loading with the stbi library, and that works fine, so I'm not sure where it's going wrong.

(the coordinates for the image is N10E099)